Induction metal melting furnace



yApril 6 1954 c. H. sTEvENsoN INDUCTION METAL MELTING FURNACE Filed March l2, 1952 Patented Apr. 6, 1954 INDUCTIONMETAL MEETING FURNACE GryfH.' Stevenson; Chicagoylll.,assignon'tcLnd bergz'Engineei-ing' Gompanygihieagmr Ill.; arcor? poration ni" illinois-l Application MarclilZ, 1952,' SerialNo. 2765177" 111Claims. 1? rIhis invention relates to -induction 4metal melting-furnaces and more 'particularly to'submerged channel type furnaces;

In submerged channel furnaces theinduction produces a1so^calledpinch effectf in they channels` the' case -offalloysi andi? in ally cases 1 forms slag' or dross-Which ten-dstozeollect inA the'lchannels and interfere with'. proper operationv of the furnace.

In'iny copendingf application Serial No.' 276,367 lediMarch .13;- 1952; Iiiavev proposedone solution tothe' problem'by supplyingan' inertfgas tothe channels;-y Tl'ie present'y invention provides another manner-of preventingI accessofair 'to the channelsin casesiwhereinert' gas-lis not available or` Wherefor 'some other. reason itsfuse is: not de* sirable:

It is, therefore, one of the objects of the present invention:toiprovidezanr induction metal l melting furnace-'inf which x air# isfrkept l outof r the channels during operation.

Anotherfobjectis to vpmvide ar furnacevinwhich theecha'nnelsa are' made 1impervious lto "airfby coverin'g` at i least*I one-surface thereof? with: an# impervious4 vitrie'di covering;

According f to onezfeaturefof the z invention,- the cha-uncle areprecastiJ of refractory f material,k are covered-onftheinouter surfaces with aY vitried impervious-covering;. and are/then enclosed or imbedded inxtheirefractory 'bodyf'of the furnace.

'Ihefaboveaandotherobjectseanddadvantages"of the'inventionfwillbefmoreueadlyfapparentwhen viewed in connection withI the accompanying drawings; in r Figure 1-E isla-fliorizontalsectinalview on the line 23-2'01 Figure'` lfofafurnace embodying the invention;

Figure 2 isl a vertical'Y section" through the furnace;L

Figure 3fis afvertic'ai sectionL througnanother type'of frnacertofwhich theinventinisfappled andi Figure 4is"an enlarged'v partial section through a 'wall of one-of the tubes:

The' inventioncis: illustrated in` FiguresY 1 l and 2 in connection' with actu/'c' chamber lfurnacefcompricing a-'boolv` llbof" ceramic material'V/hich is enclosed invv and'. supported byan outer metal shell' H: The body Ibis formed with a pair of open -vtopped chambersg l2iand-y I3 fspaced horizontally andconnectedfby channels'll'- beneath the ncrmallevelofmolt'en metal? in theI chambers. Preferably the channelsL Hl are'l formed by sep arate tubes i5 of ceramic material which are enclosed" in theceramic bocl's7 Qan-dwliich are connected to the 4chambers through daredY openings l5* formed 'in'thle body l lli To melt'tliemetal'i'n the channels andchambers an electric induction" unit provided threading the' channels'y interimediatey their ends. The unit'- as' shown comprises 'al magnetic -core I 'i vheafingrend' legSeX-tending along thez outer sides ofithe channels; center` lee" extending-l between tlie' criannelsfan'd-top 'andbottbm legs connecting theendandcenter-legs. An energizing winding notfshown isprovided-on the Corese that when the coreisfenergizeditfwill 'induceowof current through the metal f in the channels and chambers toheatand'meltthe'me'talg ltwill be noted that the inductioncoil"isY positioned entirely between thezendsfoffthe-channelsandi'between the ends of the tubes-f l so" that its magneticy center lies inn termediate -the-tubewends.

Inl the normal operation off a furnace of this type a-so-calledpincli effect occurs in the central partsof the tubes* generally in' the plane of the magnetic center` of the inductivel unit which causes the'metalfirr-thetubes to tend to flow outwardly in" beth directions fromI the center. This-eifec-t creates -afpartial y'vacuum inthe central parts of the tubes whichiwill'tendto draw air: into' the tubes? through therefiactory body Iliff-which is perviusto airi'and'through the walls of the tubes, themselves whichy are also formed cfa-refractory'orceramicmaterial and are therefore also normallypervious toair. This action WilloccurA even thoughthe body is substantially enclosed in .a shell' H i which .i'sairtighti since the air will permeate the ceramic body lil` through the upperA portions of the Walls of, chambers lland' I3'.

According.Y to the present invention, entrance of"air into the channels during operation is prevented, by so forming, the tubes i 5. thatthey. will be' airtight; For this purpose; atA .leasttne outer surfaces of tlietub'es areecoated'or impregnated With'a material which will'frm an airtight covering thereon so that air cannot be drawn through the tube walls. One convenient manner of accomplishing this is to dip or otherwise coat the outer surfaces of the tubes with a vitreous enamel which can be drawn into the pores of the tubes if desired by subjecting the tubes to vacuum. Thereafter, the tubes are baked to vitrify or fuse the enamel material, thereby to form a continuous impervious covering over the tube walls. The tubes can thereafter be mounted in the refractory body I in the usual manner.

Since in operation the pinch effect occurs only in the central parts of the tubes, air tends to be drawn into the channels only through the tube walls themselves. Therefore by making the tube walls impervious to air access of air to the molten metal is prevented so that the metal will be melted without oxidation and with a minimum formation of slag or dross.

For many types of metals such as aluminum or magnesium, which might react with the vitreous material the outer surface of the tubes is covered. With other metals such as certain types of ferrous metals and various brass ccmpositions which do not react with the vitreous material the inner and outer surfaces of the tubes may both be covered in the same manner to provide a somewhat more effective seal. Alternatively the channels I4 may be formed directly in the refractory body I0 and may be covered with a vitrified material before placing the furnace in service.

Figure 4 illustrates in enlarged section the general character of the tubes I5 when one wall only is covered as described. As there shown the tube l wall indicated at I8 is of refractory material which may be compact and cured to form a complete self supporting tube. The outer surface of the tube as indicated at I9 is covered and at least partially impregnated by a vitriied material which may be formed as described above by coating and partially impregnating the surface with a vitreous enamel which is thereafter heated to fuse the particles. The covering I8 forms a continuous fused surface which is impervious to air and which will prevent entrance of any air into the channels while the metal contacts only the inner engaged surfaces of the refractory tubes.

Figure 3 illustrates application of the invention to a single chamber vertical type furnace which comprises a refractory body 20 enclosed in and supported by a metal shell 2I. At its upper end the body is formed with a chamber 22 to hold the molten metal. Below the chamber a looped channel 23 extends downwardly into the body 2|) and has its ends communicating with the bottom of the chamber. The channel 23 may be formed by a looped ceramic tube 24 which is enclosed in the ceramic body 20.

Heat is supplied by an electric induction unit including a core 25 threaded around the channel 24 and lying completely between the ends of the channel. The core 25 carries an energizing winding not shown.

In operation of this type of furnace, the pinch effect referred to above will occur in those portions of the channel 23 which register with the magnetic center of the induction unit and will tend to draw air into the channel. To prevent this the tube 24 may be covered with a vitriiied covering as described above, which is impervious to air.

In the event there should be anyV leakage through the channel walls due, for example, to cracks or other openings in the vitrifled covering,

entrance of air into the channels can still be prevented by supplying inert gas to the ceramic bodies IIJ or 2U to envelope the channels. Thus, if there is any leakage the inert gas rather than air will be drawn into the channels and there will be no oxidation of the metal. Vitrifying the channels as described is advantageous even when the use of an inert gas is desirable since even a partial vitrification of the channel walls will substantially reduce the amount of gas drawn into the channels.

While several embodiments of the invention have been shown and described in detail it will be understood that these are illustrative only and are not to be taken as a definition of the scope of the invention, reference being had for this purpose to the appended claims.

What is claimed is:

1. In an induction metal melting furnace, an elongated tube formed of electrically non-conducting refractory material which. is normally pervious to air and adapted to contain molten metal, an electric induction unit around the tube with its magnetic center intermediate the ends of the tube to induce heating current in the metal in the tube, and an air impervious covering on 'the tube to prevent flow of air through. the tube into the metal therein.

In an induction metal melting furnace, an elongated tube formed of electrically non-conducting refractory material which is normally pervious to air and adapted to contain molten metal., an electric induction unit around the tube with its magnetic center intermediate the ends of the tube to induce heating current in the metal the tube, and a vitriiied covering on at least one surface of the tube to make the tube Wall impervious to air.

3. An induction metal melting furnace comprising a body of electrically non-conducting refractory material formed with a chamber to hold molten metal, a tube formed of electrically non-conducting refractory material which is normally pervious to air communicating with the chamber and enclosed in the body of refractory material, an electric induction unit around the tube with its magnetic center intermediate the ends of the tube to induce heating' current in the metal in the tube, and a covering on at least one surface of the tube which is impervious to air.

4. An induction metal melting furnace comprising a body o1' electrically non-conducting refractory material formed with a chamber to hold molten metal, a tube formed of electrically nonconducting refractory material which is. normally pervious to air communicating with the chamber and enclosed in the body of refractory material which is normally pervious to air communicating with the chamber and enclosed in the body of refractory material, an electric induction unit around the tube with its magnetic center intermediate the ends of the tube to induce heating current in the metal in the tube, and a vitrifled covering which is impervious to air on the cute surface of the tube. 5. An induction metal melting furnace comprising a body of electrically non-conducting refractory material formed with a pair of horizontally spaced chambers, tubes formed of electrically non-conducting refractory material which is normally :pervious to air enclosed in the body of refractory material and connecting the chambers below the normal level of molten metal therein, an electric induction unit threading the tubes with its magnetic center intermediate the ends of the tubes to induce heating current in the metal in the tubes, and a covering of material which is impervious to air on at least one surface of the tubes.

6. An induction metal melting furnace comprising a body of electrically non-conducting refractory material formed with a pair of horizontally spaced chambers, tubes formed of electrically non-conducting refractory material which is normally pervious to air enclosed in the body of refractory material and connecting the chambers below the normal level of molten metal therein, an electric induction unit threading the tubes with its magnetic center intermediate the ends or the tubes to induce heating current in the metal in the tubes, and a vitrified covering which is impervious to air on the outer surface of the tubes.

7. An induction metal melting furnace comprising a body of electrically non-conducting refractory material formed in its upper part with an open topped chamber, a looped tube enclosed in the body with its ends communicating with the lower part of the chamber, the tube being formed of electrically non-conducting refractory material which is normally pervious to air, an electric induction unit threading the looped tube, and a covering of material which is impervious to air on at least one surface of the looped tube.

8. An induction metal melting furnace comprising a body of electrically non-conducting refractory material formed in its upper part with an open topped chamber, a looped tube enclosed in the body with its ends communicating with the lower part of the chamber, the tube being formed of electrically non-conducting refractory material which is normally pervious to air, an electric induction unit threading the looped tube, and a vitried covering which is impervious to air on the outer surface of the looped tube.

9. In an induction metal melting furnace, an elongated tube of non-metallic, non-conducting material, and an electric induction unit around the tube with its magnetic center intermediate the ends of the tube, the tubing having at least one surface which is fused to make the tube wall impervious to air.

10. In an induction metal melting furnace, an elongated tube of non-metallic, non-conducting material, the walls of the tube being impervious to the passage of gas, and an electric induction unit around the tube with its magnetic center intermediate the ends of the tube.

11. An induction metal melting furnace comprising a body of refractory material formed with a chamber to hold molten metal, an elongated tube formed of non-metallic, non-conducting material communicating with the chamber and enclosed in the body of refractory material, the walls of the tube being impervious to the passage of air, and an electric induction unit around the tube with its magnetic center intermediate the ends of the tube.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 756,891 Potter Apr. 12, 1904 1,152,586 Wright Sept. 7, 1915 1,803,282 Morgan Apr. 28, 1931 1,851,575 Greene Mar. 29, 1932 1,917,849 Northrup July 11, 1933 2,156,608 Schon et al. May 2, 1939 2,402,582 Scali June 25, 1946 2,540,744 Lillienberg Oct. 1, 1948 2,585,791 Klein Feb. 12, 1952 

